1. Field of the Invention
The present invention relates to a semiconductor light-emitting device that emits light in the green color to red-color bands, an electrode for the semiconductor light-emitting device, a fabrication method of the electrode, an LED lamp using the semiconductor light-emitting device, and a light source using the LED lamp.
2. Description of the Prior Art
As light-emitting devices such as a light-emitting diode (LED) and a laser diode (LD) which emit light in the reddish-orange band, a light-emitting device including a light-emitting portion structure formed of a mixed crystal layer of (AlXGa1-X)YIn1-YP (0xe2x89xa6Xxe2x89xa61, 0 less than Y less than 1) has heretofore been known, for example, in JP-A HEI 8(1996)-83927. The light-emitting device disclosed in this publication of the unexamined application is constructed in such a manner that a transparent conductive film made of indium tin oxide is stacked on the surface of the light-emitting portion made of the mixed crystal layer of (AlXGa1-Y)YIn1-YP and that an upper plane electrode is formed on the transparent conductive film. With this structure, current from the upper plane electrode is diffused to a region as wide as possible on the surface of the light-emitting portion via the transparent conductive film.
However, in the conventional light-emitting device, ohmic contact between the transparent conductive film and the surface of the light-emitting portion cannot be achieved sufficiently, and this is a main cause to increase a forward current and degrade service life characteristics. In order to improve this point, a window layer of JP-A HEI 11(1999)-17220, for example, is formed on the surface of a light-emitting potion, and a contact layer is formed on this window layer. Furthermore, a transparent conductive film (a conductive transparent oxide layer) made of indium tin oxide is stacked on the contact layer, and an upper plane electrode (an upper layer electrode) on the transparent conductive film, thus constituting a light-emitting device. Thus, a current from this upper plane electrode is diffused to a region as wide as possible on the surface of the light-emitting portion via the transparent conductive film, contact layer and window layer.
In the light-emitting device disclosed in JP-A HEI 11(1999)-17220, however, though the ohmic contact between the transparent conductive film and the semiconductor layer is improved, since the contact layer is provided, emitted light is absorbed by this contact layer. Accordingly, a high luminance light emission cannot be sufficiently achieved, and a light-emitting efficiency is not improved.
The present invention has been proposed considering the aforementioned problem. An object of the present invention is to provide a semiconductor light-emitting device which is capable of realizing a good ohmic contact between an electrode and a semiconductor layer and significantly improving a light-emitting efficiency without absorption of emitted light, an electrode for the semiconductor light-emitting device, an LED lamp using the semiconductor light-emitting device, and a light source using the LED lamp.
To achieve the above object, the present invention provides a semiconductor light-emitting device which comprises: a semiconductor substrate having a rear surface on which a first electrode is formed; a semiconductor layer including a light emitting portion, that is formed on the semiconductor substrate; dispersed electrodes formed individually on a part of a surface of the semiconductor layer and making ohmic contact with the semiconductor layer; a transparent conductive film formed so as to cover the surface of the semiconductor layer and the dispersed electrodes, the transparent conductive film electrically conducting with the dispersed electrodes; and a pad electrode formed on a part of a surface of the transparent conductive film, the pad electrode electrically conducting with the transparent conductive film.
The semiconductor light-emitting device of the invention includes a configuration in which the dispersed electrodes are formed on the semiconductor layer surface around the pad electrode when viewed from above.
The semiconductor light-emitting device of the invention includes a configuration in which the dispersed electrodes are formed on the semiconductor layer surface at portions where the dispersed electrodes do not overlap the pad electrode when viewed from above.
The semiconductor light-emitting device of the invention includes a configuration in which the dispersed electrodes are not formed on the semiconductor layer surface at portions where the dispersed electrodes overlap the pad electrode when viewed from above.
The semiconductor light-emitting device of the invention further includes a feature that the total plane area of the dispersed electrodes is smaller than the area of the pad electrode.
The semiconductor light-emitting device of the invention includes a feature that the total plane area of the dispersed electrodes is 3% to 30% of the effective light emitting area.
The semiconductor light-emitting device of the invention includes a feature that the light-emitting portion is made of AlGaInP.
The semiconductor light-emitting device of the invention includes a feature that the semiconductor layer is formed by the metal organic chemical vapor deposition (MOCVD).
The semiconductor light-emitting device of the invention includes a feature that the transparent conductive film is made of indium tin oxide (ITO).
The semiconductor light-emitting device of the invention further includes a configuration in which the pad electrode is formed on the semiconductor layer via the transparent conductive film, but there is no transparent conductive layer on the surface of the pad electrode subjected to wire-bonding.
The semiconductor light-emitting device of the invention includes a configuration in which the pad electrode is formed on the semiconductor layer surface at the center when viewed from above.
The present invention further provides an electrode for the semiconductor light-emitting device, which comprises: dispersed electrodes formed individually on a part of a surface of the semiconductor layer including a light emitting portion, the dispersed electrodes making ohmic contact with the semiconductor layer; a transparent conductive film formed so as to cover the surface of the semiconductor layer and the dispersed electrodes, the transparent conductive film electrically conducting with the dispersed electrodes; and a pad electrode formed on a part of a surface of the transparent conductive film, the pad electrode electrically conducting with the transparent conductive film.
The electrode of the invention for the semiconductor light-emitting device includes a configuration in which the dispersed electrodes are formed on the semiconductor layer surface around the pad electrode when viewed from above.
The electrode of the invention for the semiconductor light-emitting device includes a configuration in which the dispersed electrodes are formed on the semiconductor layer surface at portions where the dispersed electrodes do not overlap the pad electrode when viewed from above.
The electrode of the invention for the semiconductor light-emitting device further includes a feature that the total plane area of the dispersed electrodes is smaller than the area of the pad electrode.
The electrode of the invention for the semiconductor light-emitting device includes a feature that the total plane area of the dispersed electrodes is 3 to 30% of the effective light emitting area.
The electrode of the invention for the semiconductor light-emitting device includes a feature that the transparent conductive film is made of indium tin oxide.
The electrode of the invention for the semiconductor light-emitting device further includes a configuration in which the pad electrode is formed on the semiconductor layer via the transparent conductive film, but there is no transparent conductive layer on the surface of the pad electrode subjected to wire-bonding.
The electrode of the invention for the semiconductor light-emitting device includes a configuration in which the pad electrode is formed on the semiconductor layer surface at the center when viewed from above.
The invention further provides a method for fabricating the electrode for the semiconductor light-emitting device comprising: a first step of forming dispersed electrodes individually on a part of a surface of a semiconductor layer including a light emitting portion, the dispersed electrodes making ohmic contact with the semiconductor layer; a second step of forming a transparent conductive film so as to cover the surface of the semiconductor layer and the dispersed electrodes, the transparent conductive film electrically conducting with the dispersed electrodes; and a third step of forming a pad electrode on a part of a surface of the transparent conductive film, the pad electrode electrically conducting with the transparent conductive film.
The electrode fabrication method of the invention includes a configuration in which the dispersed electrodes are formed on the semiconductor layer surface around the pad electrode when viewed from above.
The electrode fabrication method of the invention includes a configuration in which the dispersed electrodes are formed on the semiconductor layer surface at portions where the dispersed electrodes do not overlap the pad electrode when viewed from above.
The electrode fabrication method of the invention includes a configuration in which the dispersed electrodes are not formed on the semiconductor layer surface at portions where the dispersed electrodes overlap the pad electrode when viewed from above.
The electrode fabrication method of the invention includes a feature that the transparent conductive film is made of indium tin oxide.
The electrode fabrication method of the invention includes a feature that the transparent conductive film is formed by a spattering method, and the pad electrode is formed by a vapor deposition method.
The electrode fabrication method of the invention further includes a configuration in which the pad electrode is formed on the semiconductor layer via the transparent conductive film, but there is no transparent conductive layer on the surface of the pad electrode subjected to wire-bonding.
The invention further provides an LED lamp using the semiconductor light-emitting device.
The invention further provides a light source using the LED lamp.
In the present invention, since the dispersed electrodes are formed on a part of the surface of the semiconductor layer, as described above the electrical resistance between the semiconductor layer and the dispersed electrodes is made much smaller than that between the transparent conductive film and the semiconductor layer. Since a major part of a driving current supplied from the pad electrode flows through a path between the semiconductor layer and the dispersed electrodes having a smaller electrical resistance, light can be emitted from the light-emitting portion around the dispersed electrodes. Furthermore, since the major dispersed electrodes are disposed so as not to overlap the pad electrode, no light emission toward immediately below the pad electrode occurs. Therefore, a major part of light can be emitted upward without being intercepted by the pad electrode. Thus, the emission efficiency can be improved to a great extent.
The above and other objects, features and advantages of the present invention will become apparent from the description of the preferred embodiments of the invention made herein below with reference to the accompanying drawings.